Quirks of Human Anatomy: Why Evolution Left Us with Flaws

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📝 Article information

🎯 Hook

Ever wonder why you cannot wiggle your ears, why you choke on water sometimes, or why childbirth is so painful? It is not bad design. It is evolution’s version of “good enough for now” that stuck around.

💡 One-sentence takeaway

Human anatomical flaws like inverted retinas, wisdom teeth, and choking hazards are evolutionary holdovers that made sense for our ancestors but cause problems today. We are stuck with them because the cost of changing them is too high.

📖 Summary

Lewis Held’s Quirks of Human Anatomy goes through the weird parts of human anatomy. Figure Legends 6 covers 13 specific flaws, from silly ones like ear-wiggling muscles to lethal ones like ectopic pregnancy.

The main idea is “bislagiatt,” which means “but it seemed like a good idea at the time.” Evolution does not design from scratch. It tinkers with what already exists. When our chordate ancestors dragged their eyespots inside to protect them, they accidentally inverted the retina. When our jaw shortened over time, wisdom teeth did not get the memo and kept trying to erupt into too little space.

Held covers several examples:

  • The inverted retina and blind spot: photoreceptors sit behind ganglion cells, so light has to pass through layers of cells first. It works, but it is not optimal.
  • Choking: our epiglottis has to choose between air and food, so when it fails, we choke. Babies can breathe and suckle at the same time because their larynx is higher, but we lose that ability as we grow.
  • Childbirth: the tight fit between the baby’s head and the mother’s pelvis causes pain and risk. The baby has to rotate 90 degrees to get through.
  • Wisdom teeth, back pain, vasa deferentia that are too long, urethra running through the prostate, May-Thurner syndrome (left leg blood clots more often), ectopic pregnancy.

He also compares human eyes to fly eyes. Flies have rhabdomeric photoreceptors, humans have ciliary ones, and our retinas are backwards while theirs are not. The article brings in William Blake’s human-fly chimera drawings because humans and flies share a common bilaterian ancestor over 500 million years ago.

🔍 Insights

Evolution tinkers, it does not engineer. It cannot start from scratch, so it repurposes old structures. The inverted retina is a mistake made when chordates moved their nervous system inside. We cannot reverse it now because photoreceptors rely on the pigment layer behind them.

“Good enough” sticks. The choking hazard has not killed enough humans to drive a fix. Most people do not choke to death often enough for natural selection to favor a separate breathing tube.

Developmental quirks become features. Fontanels (soft spots) in baby skulls existed to let skull bones grow. They ended up being useful for letting the skull deform during childbirth. Evolution co-opted an existing trait for a new use.

Humans and flies are twins separated at birth. Despite looking nothing alike, we share the same genetic toolkit for building eyes, nerves, and body plans. The differences are just tweaks to the same base code.

This connects to evolutionary medicine. Many modern health issues like back pain, wisdom teeth impaction, and choking are evolutionary mismatches, not individual failures. The question of “intelligent design” also comes up. If we were designed, why would we have a blind spot, or a urethra that runs through a prostate that can enlarge and block urine flow?

The exaptation concept matters here. Traits that evolve for one purpose get repurposed for another. The fontanels are a clear example.

💬 Quotes

  1. “To make a lung with a piece of esophagus sounds very much like tinkering.” – François Jacob, explaining evolutionary flaws.

  2. “But it seemed like a good idea at the time.” – The “bislagiatt” principle, explaining how flawed traits persist.

  3. “We are all twins separated at birth.” – Held, on humans and flies sharing a common ancestor.

  4. “The problem with having air bypass the mouth entirely, of course, is that it precludes talking.” – On why babies lose the ability to breathe and suckle at the same time.

⚡ Applications

For medical students:

Study evolutionary anatomy to understand why structures are the way they are, not just memorize their positions. Recognize that many “flaws” are holdovers, so patient symptoms might trace back to evolutionary mismatches.

For general readers:

Stop blaming yourself for wisdom teeth pain or back pain. It is not bad luck, it is evolution. Understand that “normal” anatomy is not “optimal” anatomy.

For biology teachers:

Use these quirks to teach evolution. Nothing demonstrates tinkering better than a backwards retina. Compare human and fly eyes to show how the same genetic toolkit produces different results.

📚 References

  • Held, Lewis I. Jr. Quirks of Human Anatomy. Cambridge University Press.
  • Jacob, François. “Evolution and Tinkering.” Science, 1977.
  • SDB Online: Figure Legends 6

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